1. Field of the Invention
This invention relates to an apparatus for reproducing an information signal with a plurality of rotary heads from a record bearing medium on which the information signal and pilot signals are recorded in many tracks which are formed in parallel to each other.
2. Description of the Related Art:
Techniques for reduction in size and an increase in recording density of magnetic recording and/or reproducing apparatuses have greatly advanced during recent years. VTRs having many magnetic heads arranged on a compact rotary drum have come to make their debut on the market. With regard to high density recording, many VTRs are now arranged to permit recording over a longer period of time on the conventional magnetic tape by reducing the tape travel speed to 1/2 or 1/3 thereof and recording track pitch also to 1/2 or 1/3 with the width of heads narrowed.
FIG. 1 of the accompanying drawings shows by way of example a compact drum having many magnetic heads mounted thereon as mentioned above. The illustration includes the rotary drum 15; tape guide posts 16 and 17; a magnetic tape employed as a magnetic record bearing medium; and magnetic heads A, B, C and D. The heads A and C are arranged to have the same azimuth angle and the heads B and D each to have another common azimuth angle.
Each of the magnetic heads A, B, C and D begins recording at a point near the tape guide post 16 in the position where the head A is shown in FIG. 1. Then, one field portion of a video signal is completely recorded with the head A having turned around 270 degrees coming to the position where the head D is shown in the drawing. When the magnetic head A thus completes the recording, for example, the magnetic head B which is disposed 90 degrees ahead of the head A is located at the record start point and thus begins recording at the same time as the completion of recording by the head A. Recording is thus performed by the magnetic heads in the order of the heads as follows: A - B - C - D. Recording tracks are then formed in a pattern as represented by FIG. 2.
In cases where the magnetic heads are arranged to have a narrower width to be suited for a recording mode having a slower tape travel speed, if recording is performed in an ordinary recording mode allowing the tape to travel at an ordinary speed, there arise guard bands between adjacent recording tracks as shown in FIG. 3.
In reproducing a recorded signal with a VTR of the kind performing tracking control by a known method called a four-frequency method, pilot signals are reproduced not only from a recording track which is under control and is mainly traced by a reproducing magnetic head but also from other tracks adjoining the mainly traced track on both sides thereof. A control signal for tracking control is obtained by comparing the reproduced levels of two different pilot signals which are recorded in the two adjoining tracks. The tracking control is thus accomplished in accordance with the control signal.
Then, in case that the recording tracks having the above stated guard bands interposed in between them are traced by the narrow head, the tracking control cannot be adequately accomplished as it is sometimes impossible to obtain the reproduced pilot signal at a sufficiently high level from the above stated two adjoining tracks.
To solve this problem, a technique has been contrived for the VTR of the kind having the head arrangement as shown in FIG. 1. to obtain an adequate tracking control signal by using two magnetic heads disposed ahead and behind a video signal reproducing head for obtaining the pilot signals from the two adjoining tracks. A similar technique has been disclosed in U.S. patent application Ser. No. 805,959, filed on Dec. 5, 1985, now abandoned. The details of this technique are as follows:
In the case of the VTR having four magnetic heads as shown in FIG. 1, for example, each head is disposed away from another a distance corresponding to 1/3 field portion of the video signal in the longitudinal direction of the recording tracks. Therefore, as shown in FIG. 4, the magnetic head D obtains a pilot signal within a 1/3 field area from the start point of a front track and the magnetic head B obtains another pilot signal within a 1/3 field area before the end of a rear track when the magnetic head A is reproducing the video signal from another 1/3 field area located in the middle of a mainly traced track.
With two different pilot signals reproduced from the two adjoining tracks in this manner, a tracking control signal is obtained by comparing these pilot signals with each other. FIG. 5 is a chart showing a timing at which use of the magnetic heads is switched from one head over to another during a reproducing operation. In FIG. 5, hatched parts represent a video signal reproducing period. Parts "a" and "b" represent periods during which the pilot signals are reproduced from the front and rear tracks for obtaining the tracking control signal.
Generally, VTRs are arranged to have interchangeability among them. A video signal recorded on a magnetic tape by one VTR is sometimes reproduced by another VTR. In that instance, the recording direction of recording tracks on the magnetic tape sometimes differs from the scanning locus of a reproducing magnetic head. In some cases, for example, the linearity of the scanning locus of the head is impaired in relation to recording tracks.
The pilot signals from the adjoining tracks are obtainable by the front and rear heads only while the reproducing heads is tracing the 1/3 field area located in the middle of the main track. Therefore, in the event of the impaired linearity, tracking control cannot be adequately accomplished. Then, the reproduced video signal deteriorates to lower the quality of a reproduced picture.